Lumber production requires a series of operations including bucking logs into lengths, debarking the logs, scanning the logs for optimal cutting pattern, canting the logs by squaring up the sides, cutting the canted log into flitches or boards, edging the boards, etc.
Each of the operations has its own peculiarity and one of the objectives and/or challenges of a lumber mill is to coordinate the operations so as to maximize production. The particular operations to which the present invention is directed is the canting and sawing operations.
Canting, as contemplated herein for the preferred embodiment, involves feeding of a two-sided cant (flattened on the top and bottom) through chipping heads located to flatten the opposed sides. The chipping heads are typically rotating disks that each carry specialized knives which generate the opposed flat parallel sides. The cant (now having all four sides flattened), is then sawn into boards. The saws that accomplish this operation are typically multiple saw blades (a gang saw) spaced apart the desired width of the boards that are to be sawn from the cant.
The feeding process for this combination of canting and sawing operations involves (a) placing the two-sided cant at the entry of the canter, (b) setting the chipping disks of the canter to the desired spacing, (c) feeding the cant through the canter and then onto a conveyor, (d) positioning the four-sided cant on the conveyor to align the cant with the gang saw blades, and (e) feeding the canted log through the saw.
Inefficiency in the operation of the canter and saw in part results from the fact that the canter is capable of canting a log at a feed rate (e.g., 400 feet per minute) that is substantially greater than the feed rate that can be tolerated by the saws (e.g., 255 feet per minute). To slow the speed of the canter to match the speed of the saw is an unacceptable solution. Heretofore, sawmills would typically provide one canter for two saws as a way to maximize the production of the canter.
Not considered in the above two-saws-for-one-canter solution is the substantial gap that exists between the cants as they exit the canter. As described above, each log that is to be canted requires a different setting of the chipping disks. The new setting cannot commence until the prior cant has completely passed through the canter. The time required to reset the canter and place a following cant at the entry to the canter results in a spaced feeding of the cants through the canter. The cants exit the canter at spaced intervals, e.g., an end-to-end gap between the cants of 12 feet or more. The saw blade settings remain the same from one cant to the next. Some spacing is required to adjust the feed rollers that control entry into the saws but nothing like the gap required by the canter. A one-foot gap between cants is acceptable for sawing.
The problem of inefficient utilization of the saws is aggravated by having to stop or slow the conveyance of the cants while the cants are being aligned with the saws. Considering this time for alignment in addition to the lengthy gaps between the cants, saws are sawing only about half of the time. Yet the industry has heretofore concluded that it takes two of the saws to accommodate a single canter running at optimum speed.